The Rarest Snail in the World

What do recently retired scientists do for six weeks on a tiny Caribbean island? My husband and I are fortunate enough to have a holiday home on Little Cayman, where we spend our time swimming, snorkeling, gardening and walking. We supplement our activities with that staff of life, reading. And we go hunting for the rarest snail in the world.

Even before retirement, we had started building a library of books about the Cayman Islands. Little Cayman is about 15 kilometers long by two kilometers wide and has about 170 permanent human residents, so facilities are limited. There is no bookstore and the only library is a book exchange—heavy on beach books and thrillers—at the National Trust House. One of the best books we own about the Cayman Islands is a large compendium called The Cayman Islands: Natural History and Biogeography, published in 1994. Among other topics, it covers geology, vegetation, birds, invertebrates, reptiles and fossils. We dip into various chapters to answer our questions or sometimes simply to increase our knowledge of Little Cayman’s natural history.

That’s how we learned about Cerion nanus, the rarest snail in the world. That’s a big claim for a little snail only about a centimeter long. Cerion is a common genus of air-breathing land snails in the West Indies and the Florida Keys. Different species within the genus either have no common name or are lumped together as “peanut snails” for their general shape. The most common species on Little Cayman, Cerion pannosum, is everywhere: on grasses, bushes and trees, and lying dead on the beach. The second species on Little Cayman, C. nanus, is a most uncommon snail. When we read about C. nanus in Mike Hounsome’s chapter on terrestrial invertebrates in The Cayman Islands, we were hooked. As a young man, Mike had participated in the joint Royal Society and Cayman Islands Government Expedition to Little Cayman in 1975, when the island was little known scientifically. The permanent population then consisted of 18 people, “all of whom,” Mike later joked with us, “seemed to be named Bodden” (the name of one of the Cayman Islands’ most prominent families). Mike is an ornithologist, but, because there was another ornithologist on the expedition, he became responsible for all animals that weren’t birds—including snails.